Inherently concrete-compatible carbon sorbents for mercury removal from flue gas

ABSTRACT

A sorbent composition and process of making sorbent designed for the removal of contaminants from flue gas and subsequent use in cement or concrete formulations are discussed. The sorbent composition comprises a coal feed stock prepared to have a total BET surface area of at least 350 m 2 /g, and wherein the sorbent has a cumulative surface area less than 10 m 2 /g for pore diameters between 0.01 and 0.1 microns, a cumulative pore volume less than 0.055 cc/g for pore diameters between 0.01 and 0.1 microns, or both.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/481,819, filed Jun. 10, 2009, which claims priority to U.S.Provisional Patent Application No. 61/060,225 filed on Jun. 10, 2008 andU.S. Provisional Patent Application No. 61/073,112 filed on Jun. 17,2008.

BACKGROUND OF THE INVENTION

The preferred method of removing mercury from coal-fired power plantflue gas streams is to inject a sorbent. The preferred sorbent is aporous carbonaceous char, typically an activated carbon. After thecarbon is injected into the flue gas stream, it is captured by theparticulate capture devices in the power plant and becomes part of thefly ash. Many utilities sell the ash to companies that service thecement and concrete industry which use the ash as a cement substitute.However, the presence of carbon in the fly ash can adversely affect thequality of cement and concrete that is made from fly ash since it tendsto adsorb the foaming agent—commonly called an “AEA” or air-entrainmentadmixture—used in making the concrete. AEA's such as the vinsol resinMB-VR™, are used to create air voids in the concrete which make theconcrete better able to contract and expand during freeze-thaw cycles.Without the air voids, the concrete is more likely to crack and spall.The problem, then, is that carbon, being a good sorbent, adsorbs andremoves the foaming agent and thus tends to make the concrete moresusceptible to cracking during freeze-thaw cycles. Sorbents other thancarbon may be expected to produce similar outcomes. Excessive amounts ofthe foaming agent can be added to overcome this problem at the point ofconcrete manufacture, but the cost is often prohibitive and the testingthe end-user must employ to determine the specific amount istime-consuming, ill-defined, and inconvenient. Where concrete-compatiblecarbons have been used in the prior art, they have either cost or supplylimitations, such as Barnebey-Sutcliffe's type CA unimpregnated coconutor type CB (IAC) iodine-impregnated coconut, or they do not havesufficient mercury-removal capacity, such as RWE Rheinbraun's type HOK®lignite carbon.

To overcome this problem, a number of prior art solutions have beenproposed, most of which depend upon post-treatment of the sorbent or thesorbent/fly ash by-product. Other art, such as that found in U.S. Pat.Nos. 4,453,978; 4,828,619; 5,110,362 and 5,654,352, has attemptedunsuccessfully to resolve the problem by developing AEA's that are notadsorbed by the sorbent present in the fly ash. Still other art,particularly International Patent Application WO 2008/064360 A2 by Zhanget al., attempts to resolve the problem tautologically by identifyingand selecting a concrete-compatible sorbent using a test, called theAcid Blue Index (ABI) (that serves merely as a surrogate for a test,called the Foam Index, long used for such purposes by the concreteindustry), and calling the test a compositional parameter of the sorbentitself. Furthermore, Zhang et al. neither set nor claim boundaries foreither the minimum level of surrogate test activity consistent witheffective mercury removal or, indeed, the dimensional or compositionalrequirements of the sorbent for its primary function: the removal ofmercury from the flue gas, a requirement that may conflict with theintended concrete-compatibility of the sorbent, producing sorbents withless than desirable commercial utility.

An example of sorbent post-treatment to resolve the problem may be foundin U.S. Patent Application 20030206843/A1 by Nelson wherein a flyash-friendly sorbent is made by oxidizing a carbonaceous sorbent withvarious chemicals, ozone in particular. A similar process has beenproposed in U.S. Pat. No. 5,286,292 wherein the fly ash by-productitself is exposed to a halogen gas, preferably fluorine or chlorine, toneutralize the adsorption potential of the sorbent contained in the flyash. However, such post-treatment processes are expensive, inconvenient,and often hazardous. Additionally, in the method of Nelson some surfaceoxygen groups may be stripped off at the high temperatures of theapplication, typically near or above 300 F, rendering the treatmentprogressively ineffective during use. In U.S. Patent Application20040069186/A1, P. S Zacarias and D. B. Oates propose oxidation of thefly ash by-product itself to gasify and remove any carbon that adsorbsor otherwise interferes with the AEA. Although directed primarily tosorptive carbon that entrains with the fly ash as part of thecoal-burning process that produces the fly ash, the method could also bedirected to fly ash by-products containing carbon sorbents added asmercury capture agents. In another variation of fly ash post-treatment,M. Tardiff, R. K. Majors, and R. L. Hill disclose in U.S. PatentApplication 20040144287/A1 a process in which sacrificial agents, suchas ethylene glycol phenyl ether and sodium di-isopropyl naphthalenesulfonate, are added to the fly ash to neutralize the adsorption of theAEA by sorptive carbons contained within the fly ash. A similar processis disclosed by R. D. Young in U.S. Patent Application 20040200389/A1.In U.S. Patent Applications 20070056479/A1 and 20070056481, L. J. Grayteaches the addition of a fluorochemical surfactant to the concreteduring make-up that can preferentially stabilize the foam created by theAEA, even for fly ash containing up to 6% sorptive carbon as measured byloss on ignition (LOI), a measure of fly ash carbon content usedcustomarily in the cement and concrete industries (ASTM C618-01). Onceagain, however, these post-treatment methods represent added cost andinconvenience. Other mercury sorbents, particularly those made frommineral materials, may be more fly ash-friendly, but lack the capabilityto efficiently remove mercury and other contaminants from the flue gas,making carbon-based sorbents by far the preferred sorbents for mercurycapture and removal.

Therefore, it is an object of the present invention to provide a sorbentthat efficiently and effectively removes mercury and/or othercontaminants from flue gas streams while retaining the value of the flyash for commercial cement and concrete applications. It is further theobject of the present invention that both the contaminant adsorptiveproperties and concrete-compatible properties be provided as an integraland inherent feature of the sorbent's structure as manufactured,independent of any additional post-treatments or processes. Unlike theprior art, the present invention affords measurable upper and lowerdimensions of pore surface areas, volumes, and diameters to provideoptimal contaminant removal and concrete compatibility.

SUMMARY OF THE INVENTION

In various embodiments, the present invention is directed to a sorbentderived from a feed stock for removing mercury and other contaminantsfrom flue gas without reducing the quality of the fly ash for subsequentconcrete use. In an example the feed stock is a carbon, which isgenerally abundant and economical. During manufacture the pore size ofporous regions of the feedstock are developed to be suitable for removalof mercury and other contaminants and to produce a sorbent that limitsAEA adsorption. The sorbent is manufactured to achieve a total BETsurface area of at least 350 m²/g and to have a cumulative surface arealess than 10 m²/g for pore diameters between 0.01 and 0.1 microns and/ora cumulative pore volume less than 0.055 cc/g for pore diameters between0.01 and 0.1 microns. The pore structure is tailored such that theadsorption properties become optimally and inherently favorable tomercury removal when exposed to flue gas, yet substantially andsimultaneously unfavorable to the adsorption of AEA foaming agents whenentrained in fly ash that is used subsequently for concrete manufacture.In examples, this sorbent can present a significant savings to theelectric utility industry.

The interaction of the sorbent with the AEA during concrete manufactureis complex, involving a number of chemical and physical factors. Yet,the inventors have discovered the pore region critical to significantAEA transparency of the sorbent. Particularly a preferred carbon sorbentcan be largely independent of the type of feedstock used to make thesorbent. In examples, it does not depend upon the total adsorptioncapacity of the sorbent. Unlike the teachings of Zhang et al., porouscarbons made from even low-rank carbon feed stocks may now producesorbents with both enhanced mercury removal and concrete-compatibility.

Surprisingly, the inventors discovered the most relevant dimensional andcompositional characteristics for concrete-compatibility can berepresented not by tests, such as BET surface area that measure totaladsorption surface area, but by measurements of pore volumes and surfaceareas over a specific range of pore diameters. In particular, theinventors have discovered a critical porous region of the sorbent iswhere pore diameters range above about 0.002 microns (2 nm), andparticularly above 0.01 microns (10 nm), but below pore diameters around0.1 microns (100 nm). An advantage of the present sorbent and method isthis region has both a lower and upper limit spanning both themesoporous and macroporous regions of the pore space. It is itself theprimary compositional metric for concrete-compatibility, while BETsurface area serves as the primary compositional metric for mercuryadsorption. Since it has been demonstrated in the present invention thatBET surface area can range from around 350 m²/g to well above 1000 m²/gfor a carbon sorbent having both effective mercury removal as well asconcrete-compatibility, a discovery unknown in the prior art, a lowerlimit to BET surface area can suffice to ensure sufficient mercuryremoval capability. The inventors believe that one theory behind theirdiscovery is the porous region critical to concrete-compatibility servesmore of a kinetic than adsorptive function, thereby providing more timefor the AEA to function as it should with the mineral components of thefly ash to entrain air during mixing, at which point the AEA becomeslargely unavailable for adsorption into the carbon.

Mercury porosimetry is most often used to characterize and quantify theregion not found to be critical to concrete-compatibility, although anycomparable technique may also be used. In the present invention, thisregion has been correlated directly to a metric, called the foam test,long and widely used to distinguish concrete-compatible fromconcrete-incompatible carbon-containing flyash materials. The dimensionsof the critical region of the carbon sorbent, as well as the foam testmetric, have been found in this invention to correspond reasonably wellto the Molasses Number for carbon-based sorbents, much as Iodine Numberhas been found to correspond to BET surface area by those skilled in thecarbon arts. Therefore, in an example, the Molasses Number is useful todefine an inherently concrete-compatible carbon sorbent provided aminimum BET surface area is also specified. Since the Iodine Number isknown to those skilled in the activated carbon arts to numericallyapproximate BET surface area, the Iodine Number itself may be used tospecify the requisite minimum total surface area. Generally speaking,the region of surface area or pore volume critically affecting the AEAtransparency of the sorbent during concrete manufacture is smallcompared to the total surface area (as determined by BET surface area oras estimated by Iodine Number for carbon-based sorbents) or total porevolume (as determined by porosimetry for pore diameters above about0.003 um) of the sorbent, typically 5% or less for the sorbents claimedin this invention.

In an example, the sorbent comprises an activated carbon made frombituminous coal having an Iodine Number of at least 300 mg/g. Thesorbent is manufactured to remove mercury effectively absent anypost-treatment of the carbon to improve its effectiveness. Anythingbelow 300 mg/g may result in progressively reduced levels of mercuryremoval (N. Pollack and R. Vaughn, “Sorbent Injection: Taking theTechnology from R&D to Commercial Launch,” Paper #188, Power Plant AirPollutant Control “Mega” Symposium, Aug. 25-28, 2008, Baltimore, Md.,which is incorporated by reference herein). Since Iodine Number is knownto those skilled in the activated carbon arts to approximate the totalBET surface area of an activated carbon (H. Sontheimer, J. C.Crittenden, and R. S. Summers, “Activated Carbon for Water Treatment”Second Edition (DVGW-Forschungsstelle, 1988), p. 102, which isincorporated by reference herein), the minimum pore structure formercury retention and AEA exclusion can, therefore, also be monitored bythe development of surface area for a given carbon feedstock and a givenset of process conditions. However the lower and upper limit to IodineNumber and, therefore, to total surface area, can change depending uponthe feedstock and manufacturing process used to make the sorbent. Foractivated carbons derived from coconut, for example, Iodine Numbersabove 1000 mg/g or BET surface areas above 1000 m²/g can still produceconcrete-compatible sorbents having considerable AEA transparency whilefor other sorbent starting materials, lignite in particular, increasesin BET surface area can work quickly against development of concretecompatibility unless suitable modifications are made to themanufacturing process. However, coconut-based sorbents have much morelimited availability and may give rise to critical supply interruptions,while lignite-based carbons rapidly lose concrete-compatibility as BETsurface areas rise above about 300-350 m²/g.

In various embodiments, this invention specifies the critical porestructure of the carbon such that the properties of the sorbent areoptimized for adsorption of mercury and other contaminants from the fluegas, as well as transparency to the AEA during cement/concrete make-upand use, independent of the feedstock and process conditions used tomake the sorbent and independent of any post-production modifications toimprove the concrete-compatibility and mercury-removal capabilities ofthe sorbent. The invention thereby eliminates post-treatment costs andavoids the problems associated with the prior art by making theproperties of the sorbent itself both highly effective for contaminantremoval and inherently concrete-compatible and significantly transparentto the addition of foaming agents such as AEAs.

Those and other details, objects, and advantages of the presentinvention will become better understood or apparent from the followingdescription and embodiments thereof.

BRIEF DESCRIPTION OF THE DETAILED DRAWINGS

The accompanying drawings illustrate examples of embodiments of theinvention. In such drawings:

FIG. 1 shows FIG. 1 shows the variation in Foam Index with Iodine Numberfor carbon sorbents made from a range of carbon feed stocks and processconditions.

FIG. 2 shows the variation in Foam Index with Cumulative Pore Area forpore diameters between 0.01 and 0.1 um for carbon sorbents made from arange of carbon feed stocks and process conditions.

FIG. 3 shows the variation in Foam Index with Cumulative Pore Volume forpore diameters between 0.01 and 0.1 um for carbon sorbents made from arange of carbon feed stocks and process conditions.

FIG. 4 shows the variation in Foam Index with Cumulative Pore Area forpore diameters between 0.005 and 0.01 um for carbon sorbents made from arange of carbon feed stocks and process conditions.

FIG. 5 shows the variation in Foam Index with Cumulative Pore Area forpore diameters above 0.1 um for carbon sorbents made from a range ofcarbon feed stocks and process conditions.

FIG. 6 shows the variation in Foam Index with Cumulative Pore Volume forpore diameters between 0.005 and 0.01 um for carbon sorbents made from arange of carbon feed stocks and process conditions.

FIG. 7 shows the variation in Foam Index with Cumulative Pore Volume forpore diameters above 0.1 um for carbon sorbents made from a range ofcarbon feed stocks and process conditions.

FIG. 8 shows the variation in Foam Index with Molasses Number for carbonsorbents made from a range of carbon feed stocks and process conditions.

FIG. 9 shows the variation in Molasses Number with Cumulative Pore Areafor pore diameters between 0.01 and 0.1 um for carbon sorbents made froma range of carbon feed stocks and process conditions.

FIG. 10 shows the variation in Molasses Number with Cumulative PoreVolume for pore diameters between 0.01 and 0.1 um for carbon sorbentsmade from a range of carbon feed stocks and process conditions.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

Various embodiments of the present invention are directed to inherentlyconcrete-compatible sorbents. The sorbent, in various embodiments, isdefined by its total surface area and cumulative surface area or porevolume. In such embodiments, the sorbent has a total BET surface area ofat least 350 m²/g, and either a cumulative surface area of less than 10m²/g for pore diameters between 0.01 and 0.1 microns or a cumulativepore volume less than 0.055 cc/g for pore diameters between 0.01 and 0.1microns. Alternatively, the sorbent has both a cumulative surface areaof less than 10 m²/g and a cumulative pore volume less than 0.055 cc/gfor pore diameters between 0.01 and 0.1 microns. Preparation of thesorbent requires careful control of the sorbent pore structure toproduce an inherently concrete-compatible sorbent that is also effectivefor removal of mercury and other contaminants from the flue gas. Theoptimal pore structure is obtained when sufficient high-energyadsorption micro-pore volume is developed for effective mercury removalwithout the concurrent development of larger lower-energy poresconducive to AEA transport and adsorption. In an example, a preferredcarbon sorbent can be prepared from a broad range of carbon feed stocksand processing conditions. The sorbent has a pore volume characterizedby that which is generally achievable at a BET surface area or IodineNumber of at least 350 m²/g or 350 mg/g, respectively, and a cumulativesurface area less than 10 m²/g and/or a cumulative pore volume less than0.055 cc/g for pore diameters between 0.01 and 0.1 microns to restrictthe development of the pore region conducive to AEA transport andadsorption.

The structural and dimensional boundaries specified for the sorbents ofthe present invention may also be referenced by other parameters andtesting methods that frame the region of interest, such as a minimum andmaximum pore adsorption potentials, surface areas, volumes, and/ordiameters for mercury removal and AEA exclusion, respectively, asprovided by other conventional tests for these parameters or by anyother individual parameters or test procedures that can be functionallyand directly related to the pore regions of interest.

Generally speaking, BET surface area and, therefore, mercury removalcapabilities obtain more readily and more at the expense ofconcrete-compatibility for lower rank carbon feedstocks, such as ligniteand sub-bituminous coal, than for higher rank feedstocks, such asbituminous and anthracite coals, or high-density cellulosic feed stockssuch as coconut. The lower rank coals are, therefore, less forgiving interms of process conditions, but still effective in producing inherentlyconcrete-compatible sorbents that are also effective for the removal ofmercury and other contaminants. Although feedstock pre-treatments andchanges in processing conditions may greatly improve sorbent structuraldevelopment outcomes in these materials, they also usually increaseprocess complexity and product costs and may be less desirable in thisregard.

In various embodiments, the sorbent of the present invention wasprepared from a variety of carbon feed stocks under a variety of processconditions. All of the carbon chars were free of any post-activationtreatments or additives that might alter the inherent physical andchemical properties of the sorbent, such as the addition of halogens toimprove mercury removal capabilities or the addition of pore blockingagents such as surfactants or oxidation with oxygen or ozone to enhanceconcrete-compatibility, although the use of such additives or processesmay be useful extensions of the present invention. Series A carbons weremade from sub-bituminous coal; series B, from lignite; series C, fromcoconut char; series D, from semi-anthracite coal; and series E, frombituminous coal. The feed stocks for series A-D were activated in steamat various temperatures above 700 C without pulverization andre-agglomeration of the feed stock. The feed stock for series E waspulverized, re-agglomerated, and oxidized in air at temperatures between100 and 450 C before activation in steam at temperatures above 700 C.The carbons were then tested for their AEA foaming tendencies by use ofa foam index test.

In these examples, the number of drops of a vinsol-resin-based AEAavailable from BASF called MB-VR™ was used to indicate the concretecompatibility of the carbon in a foaming test that has had broadacceptability within the concrete manufacturing industry. Other AEAs,such as BASF's Micro-Air® and MB AE 90™, may be used in place of MB-VR™.Although they produce different numerical results, the relative rankingof foaming tendencies among different carbon sorbents does not changesignificantly. In this particular test, 2.0 grams of each carbon,pulverized to at least 95%<325 mesh, was added to 30.0 grams of a ClassC fly ash and mixed by swirling for about 20 seconds with 70.0 grams ofde-ionized water in an 8 ounce wide-mouth glass jar. Next, four drops ofthe AEA, undiluted and as received from the manufacturer, was added, andthe jar was capped and shaken vigorously for about 30 seconds. Uponopening the jar, the surface of the slurry was inspected for a foamlayer extending across and completely covering the surface that wasstable for at least a minute. If none was observed, the process ofadding 4 drops of AEA and shaking for 30 seconds was repeatedimmediately until the desired stable foam endpoint is achieved. Thetotal number of drops of AEA added to achieve the stable foam endpointwas reported as the foam index for the carbon sorbent tested. Anendpoint less than about 30 drops in the above test generally indicatesa carbon sorbent that is reasonably to marginally concrete-compatible,depending upon the type and quality of concrete desired. Twelve drops orless indicates a highly concrete-compatible carbon. Four drops orless—or the end-point of the fly ash alone containing nocarbon—indicates a carbon that is essentially transparent to the AEA.Endpoints above about 40 drops usually indicate little commercialutility for a fly ash which contains the carbon at the level tested.

The results of the carbon foam indexes were compared to various carbonproperties of each sorbent to determine if and how certain propertiesmay be tailored to produce a carbon sorbent for mercury removal fromflue gas that would also be concrete-compatible when entrained in theflue gas fly ash. The other carbon-related parameters determined forthis purpose included pore volume and surface area as a function of poresize as determined by Mercury Porosimetry (Micromeritics Test Method942/65000/03 or equivalent); Apparent Density (“AD”, Calgon Carbon TestMethod 1 or equivalent); Iodine Number (Calgon Carbon Test Method 4 orequivalent); and Molasses Number (Calgon Carbon Test Method 3 orequivalent). These data are given in Table 1. Based on the datagenerated from the examples, a dimensional window forconcrete-compatibility was found that was largely and surprisinglyindependent of feed stock or processing conditions.

TABLE 1 Foam Index Pore Pore AD Iodine# (dropsMB- Volume* Area** Carbon(g/cc) (mg/g) Molasses# VR) ™ (cc/g) (m²/g) A1 0.619 314 123 12 0.0314.170 A2 0.568 523 133 28 0.052 7.550 A3 0.479 701 204 90 0.093 14.741B1 0.689 235 118 18 0.025 3.727 B2 0.638 308 136 32 0.046 6.871 B3 0.541414 183 76 0.097 15.016 C1 0.488 912 123 12 0.025 3.714 C2 0.432 1281131 28 0.035 6.080 C3 0.345 1476 153 60 0.066 13.519 D1 0.701 649 133 280.040 8.243 D2 0.612 831 147 52 0.057 11.997 E1 0.703 601 133 8 0.0233.286 E2 0.598 928 138 28 0.033 4.953 E3 0.506 1115 168 66 0.063 11.684*cumulative pore volume for pore diameters between 0.01 and 0.1 um (10to 100 nm) **cumulative pore area for pore diameters between 0.01 and0.1 um (10 to 100 nm)

In the examples to follow, Example 1 illustrates the insufficiency ofcommon but yet measures of adsorption potential, such as Iodine Number,to define the composition of an effective mercury-removal sorbent thatis also concrete-compatible. Although useful and necessary forindicating adequacy for mercury capture and the sorption of otherpotential contaminants, the microporous region of the sorbent bearssurprisingly little relevance to the structural requirements for AEAexclusion. Example 2 shows how AEA exclusion is affected over aparticular and critical range of pore diameters, pore surface areas, andpore volumes as measured by mercury porosimetry. Example 3 illustratesthat Molasses Number can be a suitable indicator of AEA exclusion acrossa broad range of carbons made from different carbon feed stocks underdifferent processing conditions, while Example 4 shows how the criticalregion of pore diameters, pore surface areas, and pore volumes is, inturn, reasonably related to Molasses Number. Taken together, theseexamples illustrate and define the compositional parameters for asorbent that is suitable for the removal of mercury and othercontaminants from flue gas, but also largely transparent to AEA additionwhen entrained in fly ash that is subsequently used for cement andconcrete make-up.

Example 1

In this example, the relationship between Iodine Number and the foamingtendencies (AEA exclusion) of the various carbon sorbents is shown inFIG. 1. Iodine Number is normally closely related to total BETadsorption surface area and adsorption pore volume. When compared to BETsurface area, Iodine Numbers are usually within roughly 10% of the BETvalue (H. Sontheimer, J. C. Crittenden, and R. S. Summers, “ActivatedCarbon for Water Treatment” Second Edition (DVGW-Forschungsstelle,1988), p. 102, which is incorporated by reference herein). As such,Iodine Number is generally a reasonable indicator of carbon sorbentperformance in a given application. However, as shown in FIG. 1, it isclear that this parameter alone is insufficient to specify thecomposition of a concrete-compatible carbon sorbent independent of thematerial and process conditions used for its manufacture. For adequatemercury removal from flue gas some minimum Iodine Number or totalsurface area is generally necessary establishing a lower bound tosurface area for a carbon sorbent that must also be concrete-compatible.A lower limit of about 350 mg/g (Iodine Number) or 350 m²/g (BET surfacearea), or more preferably a lower limit of about 400 mg/g (IodineNumber) or 400 m²/g (BET surface area) is selected for the preferredcarbon-based sorbents (N. Pollack and R. Vaughn, “Sorbent Injection:Taking the Technology from R&D to Commercial Launch,” Paper #188, PowerPlant Air Pollutant Control “Mega” Symposium, Aug. 25-28, 2008,Baltimore, Md., vide supra).

Example 2

In this example, a relationship is established between the foamingtendencies of the various carbons (AEA exclusion) and a particularregion of the carbon pore structure above about 0.01 microns (10 nm) asdetermined, for example, by mercury porosimetry or comparabletechniques. In mercury porosimetry, elemental mercury is forced into thepore structure of the carbon under pressure. Under low pressure, thelargest pores are filled first since they offer the least resistance tothe flow of mercury. As the pressure is increased, pores withprogressively smaller diameters are filled. From the data obtainedduring a run, the pore diameters and the cumulative and differentialpore volumes and surface areas may be calculated for pore diametersroughly 0.003 microns (3 nm) and larger. In this example, it is seenthat the pore region most closely related to the foam index of thecarbon sorbent lies more in the region dominated by transport meso- andmacro-pores having diameters above about 0.01 microns (10 nm) but lessthan about 0.1 microns (100 nm), as shown by the strong correspondencebetween Foam Index and cumulative pore surface area (FIG. 2) orcumulative pore volume (FIG. 3) in this region.

Conversely, rather poor correspondence is observed for the regionbetween 0.01 microns (10 nm) and 0.005 microns (5 nm) in pore diameteror for the region above a pore diameter of 0.1 microns (100 nm) as shownin FIGS. 4 and 5, respectively, for cumulative pore surface areas, or inFIGS. 6 and 7, respectively, for cumulative pore volumes in theseregions. It should be noted that 0.002 microns (2 nm) is generallyconsidered to be the upper limit of the adsorption micro-pore region bythose skilled in the activated carbon adsorption arts.

Example 3

In this example, the relationship between Molasses Number and foamingtendencies among the various carbon sorbents is shown in FIG. 8.Molasses Number is normally indicative of the pore volume of a carbonsorbent spanning the transition between larger diameter adsorption poresand the transport pores that lead to them. Historically, the test hashad wide acceptance in the activated carbon arts, but chemical effects,such as pH, and other test variables may sometimes limit theapplicability of the results from sorbent to sorbent. Surprisingly, forconcrete-compatible applications, a relationship is seen betweenMolasses Number and the foaming tendencies of the sorbent that islargely independent of feedstock or manufacturing conditions, as shownin FIG. 8. Since the fly ash alone may produce a Foam Index of 4 to 8drops of MB-VR™, a concrete-compatible carbon sorbent is defined as onewith a foam index less than about 30 drops of MB-VR™. This would requirea sorbent with a Molasses Number less than about 150, and preferablyless than 140, by Calgon Carbon Test Method 3 or any Molasses Numberderived from other versions of the Molasses Number test that can becorrelated to the Molasses Numbers derived from Test Method 3.

Example 4

In this example a correspondence is established between Molasses Numberas measured by Calgon Carbon Test Method 3 and Cumulative Pore SurfaceArea and Volume for Pore Diameters between 0.01 and 0.1 microns (10-100nm). As shown in FIGS. 9 and 10, Molasses Number may also serve as asuitable parameter to specify the compositional parameters comprising aninherently concrete-compatible carbon sorbent for use in flue gasbeneficiation, further confirming the claim boundaries establishedbetween Foam Index and Molasses Number given in Example 3. At a MolassesNumber of around 150, the cumulative pore area in the region bounded bythese pore diameters is less than about 10 m²/g, while at a MolassesNumber of around 140, the cumulative pore area is less than about 8m²/g. Similarly, at a Molasses Number of around 150, the cumulative porevolume in the same region of pore diameters is less than about 0.055mL/g, while at a Molasses Number of around 140, the cumulative pore areais less than about 0.05 mL/g.

In other examples, the sorbent can have further additives, treatments orprocess which serve to further enhance the properties of mercury removaland/or contaminant removal from a flue gas stream and/or its utility fora subsequent cement or concrete formulation. For example the sorbent isa carbon char that further includes a halogen or halide to enhancemercury or other contaminant removal. Additionally or alternatively, thesorbent further includes a pore blocking agent to enhanceconcrete-compatibility. The pore blocking agent can include one or moresurfactants or treatment with oxygen, halogens or ozone.

While the presently preferred embodiments of the invention have beenshown and described, it is to be understood that the detailedembodiments are presented for elucidation and not limitation. Theinvention may be otherwise varied, modified, or changed within the scopeof the invention as defined in the appended claims.

What is claimed is:
 1. A process for making a concrete-compatiblesorbent, comprising the step of preparing a feedstock to have a totalBET surface area of at least 350 m²/g and to have a cumulative surfacearea less than 10 m²/g for pore diameters between 0.01 and 0.1 microns,a cumulative pore volume less than 0.055 cc/g for pore diameters between0.01 and 0.1 microns, or both.
 2. The process of claim 1 wherein thefeedstock is a carbonaceous material.
 3. The process of claim 1 furthercomprising the step of incorporating the sorbent into a cement orconcrete formulation.
 4. The process of claim 1 wherein the sorbent hasproperties inherently favorable to mercury removal yet unfavorable toadsorption of AEA foaming agents when entrained in a fly ash for use inconcrete manufacture.
 5. The process of claim 1 wherein the step ofpreparing a feedstock results with a sorbent having a total BET surfacearea of at least 400 m²/g, and a Molasses Number no greater than
 140. 6.The process of claim 1 wherein the step of preparing a feedstock resultswith a sorbent having the cumulative surface area less than 8 m²/g forpore diameters between 0.01 and 0.1 microns.
 7. The process of claim 1wherein the step of preparing a feedstock results with a sorbent havinga cumulative pore volume less than 0.05 cc/g for pore diameters between0.01 and 0.1 microns.
 8. The process of claim 1 further comprising thestep of incorporating a halogen or halide with the sorbent to enhancemercury or other contaminant removal.
 9. The process of claim 1 furthercomprising the step of incorporating a pore blocking agent with thesorbent to enhance concrete-compatibility.